How do uncompetitive inhibitors affect the apparent Km and Vmax of an enzyme, and why?

They increase both Km and Vmax because they stabilize the enzyme-substrate complex.

They increase Km and decrease Vmax because they compete with the substrate.

They have no effect on Km and Vmax because they do not bind to the enzyme.

They decrease both Km and Vmax because they bind to the enzyme-substrate complex, reducing its concentration.